This invention relates to polyurethane-polyurea compositions and, more particularly, to thermoplastic polyurethane-polymer compositions having good elasticity and stability.
Thermoplastic polyurethane-polyureas are conventionally prepared from polyols, such as polyester polyols and polyether polyols, having a functionality of approximately two and diamines having one or two reactive hydrogen atoms per amine group. Such polyurethane-polyurea compositions often have poor hydrolytic stability because of the presence of the polyester and polyether linkages in the polymer chain. Furthermore, conventional polyurethane-polyurea compositions are generally prepared from diamines whose functional groups are all or substantially all primary amine groups. The urea group resulting from the reaction between a primary amine and an isocyanate contains at least one reactive hydrogen atom and hence readily undergoes biuret formation, resulting in the production of a crosslinked polymer and a reduction in those physical properties attributable to the thermoplastic nature of the polymer. Because of the potential utility of polyurethane-polyurea compositions which are hydrolytically stable and which do not readily undergo crosslinking, a great deal of effort has been expended in research to develop polyurethane-polyurea compositions having these properties. Thus, various organic diols have been used in place of or in addition to polyester and polyether polyols. For example, U.S. Pat. Nos. 3,427,366 and 3,674,743 describe polyurethane compositions prepared from hydroxylated diene polymers which have improved hydrolytic stability.
Polyurethane-polyurea compositions have now been discovered which have good hydrolytic stability and resist degradation in elastic properties.
Accordingly, it is an object of this invention to present polyurethane-polyurea compositions which have excellent hydrolytic stability and resist loss of elasticity. It is another object of the invention to present polyurethane-polyurea compositions which have good retention of thermoplastic properties. These and other objects of the invention will become apparent from the following description and examples.